Have you tried a different Fast Charger or cable? The cable is usually the culprit, though, but it might be the wall adapter as well. Some people even reported that using a different outlet helped in a few cases, so try plugging it in to a different socket.

The first few times I charged my phone, the fast charger worked. Today, I used it to connect to my laptop then it started charging so slow! I tried to change the setting to fast charge, but each time I charge it goes back to slow charge! Help!